Six point one percent - that's how many Americans 12 and older admitted smoking pot, in the government's annual drug use survey. As we've been reporting all week, attitudes toward marijuana use have relaxed dramatically in recent years, yet that consumption rate has long hovered right around 6 percent.

NPR's Martin Kaste teamed up with Youth Radio to take a closer look at what we do and don't know about America's appetite for marijuana.

MARTIN KASTE: This fall, voters in California will decide whether to make marijuana legal - under state law, at least. And the key question is likely to be: If you legalize it, will more people smoke it?

BLOCK: It's axiomatic.

KASTE: That's John Lovell, a lobbyist for California police chiefs and an organizer for the campaign against legalization.

BLOCK: Any time you take a product, any product, from a less convenient sales forum to a more convenient sales forum, use of that product increases.

KASTE: It's axiomatic - or is it? Take the example of Seattle. In 2003, voters made marijuana the city's lowest law-enforcement priority, and researchers tracked the results. Caleb Banta-Green studies drug-use trends at the University of Washington's Alcohol and Drug Abuse Institute.

BLOCK: What we looked at were measures such as self-reported consumption measures, emergency department visits, all those types of things. And essentially, those stayed effectively flat before, during and after this initiative went into place.

KASTE: But anti-marijuana groups say this misses a more insidious effect. Liberalizing pot for adults, they say, might encourage more use among kids. They point to high rates of teen pot-smoking in places such as California's Bay Area, where medical marijuana is commonplace.

To look into this, we turned to Youth Radio. High school student and reporter Sayre Quevedo sent us this report.

SAYRE QUEVEDO: Two of my best friends, fellow 11th-graders who go to school in Berkeley, are self-described stoners.

QUEVEDO: Right now, I am breaking up the herb and putting it straight into the paper. Some people break it up into their hand, but that's just an extra step, and you lose weed.

QUEVEDO: Yeah, because like, weed's expensive, you know.

QUEVEDO: And while smoking that joint is normal for them, it's still an illegal substance. So they'll remain anonymous.

For a teenager in the Bay Area, getting pot is never a problem. I know about five kids who buy marijuana from dispensaries, but it's more common just to get pot from a friend or a classmate who deals.

QUEVEDO: I can call up 10 people right now, and they'll all have a drug dealer. You know, like, it's so, like, in and out of the Bay Area that it's just so easy to get.

QUEVEDO: As in Seattle, Berkeley voters made pot arrests the lowest priority for police, but they did it nearly 25 years earlier. Still, Berkeley school officials were shocked last year when they saw results from a statewide survey of student drug use. Sixty-three percent of the district's 11th-graders reported smoking pot in their lifetime, 20 points higher than the state average. My friend wasn't surprised.

QUEVEDO: You can get it anywhere, and that leads kids to smoke more, and that leads kids to buy more, and that leads other dealers to sell more - and then also cannabis clubs to sell more. So it's definitely growing, a lot.

QUEVEDO: But the truth is those numbers are not growing. The rate of teenage smoking in Berkeley is high, but it's also been stable in the decades since dispensaries started appearing in the city.

BLOCK: Really, honestly, like I haven't seen a marked increase or decrease either way.

QUEVEDO: That's Mark Harringer, a teacher at my school who's taught for the past decade throughout the Bay Area. He says my friend's opinion is a product of becoming more aware of other teens smoking rather than a sign of a larger trend.

BLOCK: I've even asked kids, you know, what percentage of your class do you think, you know, uses marijuana or drinks alcohol or smokes cigarettes? And more than not, they inflate the number almost triple than what the actual percentage is.

QUEVEDO: Mr. Harringer's classroom experience is backed up by other results from the California Healthy Kids Survey, the one that measured Berkeley's marijuana consumption rate. It shows teenagers perceive more of their peers are smoking pot than actually are.

KASTE: This is Martin Kaste again. What Sayre found in the Bay Area is confirmed by data in other places. So far, cities that have liberalized pot have not seen noticeable spikes in consumption. Still, those figures are spotty, and other kinds of numbers are rising. Again, Caleb Banta-Green at the University of Washington.

BLOCK: We've seen an overall increase in marijuana-treatment admissions over the last 11 years in the Seattle-Kent County area.

KASTE: More of the people getting treatment are now naming marijuana as their primary addiction. Researchers are finding similar upticks in San Francisco and Los Angeles.

Banta-Green says the cause isn't clear. It may have something to do with more probation violators being sent to treatment instead of jail when they test positive for pot.

When it comes to illegal drugs, he says, it's just hard to get reliable consumption measurements, but it's not impossible.

BLOCK: One way you could actually get that is with another project I'm working on, which is where you drug test entire cities' sewer water.

KASTE: That's right. Banta-Green is talking about urine analysis for whole cities. He's already testing sewer water in 20 cities to track levels of harder drugs. But if he can find the funding, he wants to start testing that water for marijuana, too.

Combine that technique with, say, legalization of marijuana in a whole state, and he might have the makings for a very interesting experiment.

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